Optical coupler

Abstract

An optical coupler divides signal light beam in optical transmission path at predetermined ratio. The optical coupler includes single-layer dividing film evaporated on substrate with optical film thickness being of predetermined value, the film having refractive index which is equal to or smaller than square root of refractive index of substrate, and coupler holder holding single-layer dividing film in optical transmission path to apply signal light beam to single-layer dividing film at incident angle of about 45 degrees. Alternatively, optical coupler includes dividing film made of three films having respective refractive indexes of 1.46±0.10, 1.65±0.10, and 2.30±0.10 and formed in four, five, or seven layers on substrate having refractive index of 1.51±0.10 or 3.50±0.20, each layer having optical film thickness which reduces polarization dependency of dividing ratio of dividing film, and coupler holder holding dividing film in optical transmission path to apply signal light beam to the dividing film at incident angle of about 45 degrees. Alternatively, optical coupler includes dividing film made of two films having respective refractive indexes of 1.46±0.10 and 2.30±0.10 and formed in four through fourteen layers on substrate having refractive index ranging from 1.51±0.10 to 3.50±0.20, each layer having optical film thickness which reduces the polarization dependency of dividing ratio of the dividing film, and coupler holder for holding dividing film in optical transmission path to apply signal light beam to dividing film at incident angle of about 45 degrees.

We claim: 
     
       1. An optical coupler for dividing a single light beam in an optical transmission path at a predetermined ratio, comprising: a single-layer dividing film evaporated on a substrate as a single layer of silicon-dioxide with an optical film thickness thereof ranging from 0.23λ to 0.34λ, said film material having a refractive index which is equal to or smaller than the square root of a refractive index of said substrate; and   holder means for holding said single-layer dividing film in the optical transmission path such that the signal light beam is applied to said single-layer dividing film at an incident angle of about 45 degrees.   
     
     
       2. An optical coupler according to claim 1, wherein said film material is silicon dioxide, said thickness being one of 0.23λ and 0.34λ. 
     
     
       3. An optical coupler according to claim 1, wherein said film material is silicon dioxide, said thickness being one of 0.23λ, 0.24λ, 0.27λ, 0.30λ, 0.32λ, and 0.33λ. 
     
     
       4. An optical coupler for dividing a signal light beam in an optical transmission path at a predetermined ratio to reduce polarization dependency, the signal light beam at a wavelength ranging from 1250 nm to 1600 nm, the optical coupler comprising: a single-layer dividing film evaporated on a silicon substrate as a single-layer of a film material with an optical film thickness thereof being of a predetermined value, said film material having a refractive index of 1.87 or smaller; and   holder means for holding said single-layer dividing film in the optical transmission path such that the signal light beam is applied to said single-layer dividing film at an incident angle of about 45 degrees.   
     
     
       5. An optical coupler according to claim 4, wherein said film material is silicon dioxide, said predetermined value being one of 0.23λ and 0.34λ. 
     
     
       6. An optical coupler according to claim 4, wherein said film material is silicon dioxide, said predetermined value being one of 0.23λ, 0.24λ, 0.27λ, 0.30λ, 0.32λ, and 0.33λ. 
     
     
       7. An optical coupler for dividing a signal light beam in an optical transmission path at a predetermined ratio, comprising: a dividing film made of three film materials having respective refractive indexes of 1.46±0.10, 1.65±0.10, and 2.30±0.10 and formed in four, five or seven layers on a substrate having a refractive index of 1.51±0.10 to 3.50±0.20, said layers being combined in such a combination and each having such an optical film thickness as to reduce the polarization dependency of the dividing ratio of the dividing film; and   holder means for holding said dividing film in the optical transmission path such that the signal light beam is applied to said dividing film at an incident angle of about 45 degrees.   
     
     
       8. An optical coupler according for monitoring an output signal in an optical amplifier module which includes an exciting laser diode having polarized characteristics and an erbium--doped fiber for amplifying a signal light beam emitted from the exciting laser diode, the amplified signal light beam also having polarized characteristics. 
     
     
       9. An optical coupler for dividing an incident light beam at a dividing ratio ranging from 1:4 to 1:20, comprising: a dividing film made of three film materials having respective refractive indexes of 1.46±0.10, 1.65±0.10, and 2.30±0.10 and formed in four or seven layers on a substrate having a refractive index of 1.51±0.10, each of said layers having an optical film thickness ranging from 0.01λ to 0.90λ to reduce the polarization dependency of the dividing ratio of the dividing film; and   holder means for holding said dividing film in the optical transmission path such that the signal light beam is applied to said dividing film at an incident angle of about 45 degrees.   
     
     
       10. An optical coupler for dividing an incident light beam at a dividing ratio ranging from 1:2.7 to 1:4, comprising: a dividing film made of three film materials having respective refractive indexes of 1.46±0.10, 1.65±0.10, and 2.30±0.10 and formed in four layers on a substrate having a refractive index of 3.50±0.20, each of said layers having an optical film thickness ranging from 0.10λ to 0.45λ to reduce the polarization dependency of the dividing ratio of the dividing film; and   holder means for holding said dividing film in the optical transmission path such that the signal light beams is applied to said dividing film at an incident angle of about 45 degrees.   
     
     
       11. An optical coupler for dividing an incident light beam at a dividing ratio ranging from 1:2.7 to 1:19, comprising: a dividing film made of two film materials having respective refractive indexes of 1.46±0.10 and 2.30±0.10 and formed in four to ten layers on a substrate having a refractive index of 3.50±0.20, each of said layers having an optical film thickness ranging from 0.01λ to 0.80λ to reduce the polarization dependency of the dividing ratio of the dividing film; and   holder means for holding said dividing film in the optical transmission path such that the signal light beam is applied to said dividing film at an incident angle of about 45 degrees.   
     
     
       12. An optical coupler for dividing an incident light beam at a dividing ratio ranging from 1:7.4 to 1:8, comprising: a dividing film made of two film materials having respective refractive indexes of 1.46±0.10 and 2.30±0.10 and formed in four through six layers on a substrate having a refractive index of 1.46±0.10, each of said layers having an optical film thickness ranging from 0.01λ to 1.00λ to reduce the polarization dependency of the dividing ratio of the dividing film; and   holder means for holding said dividing film in the optical transmission path such that the signal light beam is applied to said dividing film at an incident angle of about 45 degrees.   
     
     
       13. An optical coupler for dividing an incident light beam at a dividing ratio of 1:7, comprising: a dividing film made of two film materials having respective refractive indexes of 1.46±0.10 and 2.30±0.10 and formed in four layers on a substrate having a refractive index of 1.60±0.20, each of said layers having an optical film thickness ranging from 0.01λ to 0.45λ as to reduce the polarization dependency of the dividing ratio of the dividing film; and   holder means for holding said dividing film in the optical transmission path such that the signal light beam is applied to said dividing film at an incident angle of about 45 degrees.   
     
     
       14. An optical coupler for dividing a signal light beam in an optical transmission path at a predetermined ratio, comprising: a single-layer dividing film evaporated on a silicon substrate as a single-layer of silicon dioxide with an optical film thickness thereof ranging from 0.23λ to 0.34λ, said film material having a refractive index of 1.87 or smaller; and   holder means for holding said single-layer dividing film in the optical transmission path such that the signal light beam is applied to said single-layer dividing film at an incident angle of about 45 degrees.